Sorry, can’t give a link – the blog is for the internal development purpose and already contains some info I’m not allowed to disclose ;(
I have only one plugin installed – Members Only (http://wordpress.org/extend/plugins/members-only/). And I already tried deactivating it – with no luck though.
In my case the category becomes highlighted, only it’s the wrong one! When I open a post inside Category B, the menu has Caterogy A highlighted. Wtf?